In one aspect the invention relates to hydrocarbon processing. In another aspect, the invention relates to an alkylation process. In yet another aspect, the invention relates to an apparatus for carrying out an alkylation process.
Alkylation processes are often employed by the petrochemical and refining industries to produce high octane blending stocks for gasoline. In such processes, it is inevitable that a portion of the feedstock, commonly at least one isoparaffin and at least one olefin, react in a manner to form a hydrocarbon having a molecular weight higher than that of the desired alkylate product. At least a portion of this hydrocarbon comprises a polymeric material which is more soluble in acid than in hydrocarbon and is commonly referred to by the industry as acid soluble oil, or "ASO". Acid soluble oils build-up in liquid acid alkylation catalyst systems and are desirably periodically or continuously removed so as to be maintained at low levels in liquid acid alkylation catalyst systems.
It is further desirable to at least partially remove water and light hydrocarbons such as propane from alkylation systems to prevent their build-up and interference with process performance. Such materials are sometimes intentionally or unintentionally introduced into alkylation systems.
According to U.S. Pat. No. 3,721,720, issued Mar. 20, 1973 to C. C. Chapman et al, the disclosure of which is incorporated herein by reference, acid soluble oils and water can be removed from hydrogen fluoride (HF) catalyst by processing a slip stream of catalyst in a fractionator under controlled temperature and pressure conditions. The acid soluble oil stream, which is removed as fractionator bottoms, is a small stream and contains only small amounts of HF and water, ASO being the major component. The ASO stream is recycled to the refinery or passed to a disposal unit.
According to U.S. Pat. No. 3,069,483, issued Dec. 18, 1962 to R. D. Bauer, the disclosure of which is hereby incorporated by reference, excessive propane build-up in an HF alkylation system can be prevented by processing a slip stream of the hydrocarbon phase in a depropanizer.
According to U.S. Pat. No. 2,984,693, issued May 16, 1961 to J. T. Cabbage, the disclosure of which is hereby incorporated by reference, excessive propane build-up in an HF alkylation system can be prevented by charging the hydrocarbon phase to an isobutane column and the overhead from the isobutane column to a depropanizer. Controlled reboiler conditions thermally decompose organically combined fluorine predominately in the C.sub.3 -C.sub.4 range.
In U.S. Pat. No. 3,993,706, issued Nov. 23, 1976 to Mikulicz et al, the hydrocarbon phase is charged to an isobutane column and the overhead from the isobutane column is charged to a depropanizer to prevent excessive propane build-up in the alkylation system. A portion of the HF catalyst phase, the major portion of which is HF, is dissolved in the overhead from the isobutane column and enters the depropanizer. In the depropanizer, the HF is separated from the ASO and recycled. The ASO is recovered as bottoms from the depropanizer and passes to the isobutane column from which it is recovered as bottoms in a blend with alkylate product.